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World Trade Center
The World Trade Center (sometimes referred to as WTC or Twin Towers) was a complex in Lower Manhattan whose seven buildings were destroyed in 2001 in the September 11 attacks. The site is currently being rebuilt with six new skyscrapers and a memorial to the casualties of the attacks. The original World Trade Center was designed by Minoru Yamasaki in the early 1960s using a tube-frame structural design for the twin 110-story towers. In gaining approval for the project, the Port Authority of New York and New Jersey agreed to take over the Hudson & Manhattan Railroad which became the Port Authority Trans-Hudson (PATH). Groundbreaking for the World Trade Center took place on August 5, 1966. The North Tower (1) was completed in December 1970 and the South Tower (2) was finished in July 1971. Construction of the World Trade Center involved excavating a large amount of material which was used in making Battery Park City on the west side of Lower Manhattan. The complex was located in the heart of New York City's downtown financial district and contained 13.4 million square feet (1.24 million m2) of office space.12 The Windows on the World restaurant was located on the 106th and 107th floors of the North Tower, while the Top of the World observation deck was located on the 107th floor of the South Tower. Other World Trade Center buildings included the Marriott World Trade Center; 6 World Trade Center, which housed the United States Customs; and 7 World Trade Center, which was built in the 1980s. The World Trade Center experienced a fire on February 13, 1975 and a bombing on February 26, 1993. In 1998, the Port Authority decided to privatize the World Trade Center, leasing the buildings to a private company to manage, and awarded the lease to Silverstein Properties in July 2001. On the morning of September 11, 2001, al-Qaeda-affiliated hijackers flew two 767 jets into the complex, one into each tower, in a coordinated suicide attack. After burning for 59 minutes, the South Tower (2) collapsed, followed a half-hour later by the North Tower (1), with the attacks on the World Trade Center resulting in 2,750 deaths. 7 World Trade Center collapsed later in the day and the other buildings, though they didn't collapse, had to be demolished because they were damaged beyond repair. The process of cleanup and recovery at the World Trade Center site took eight months. The first new building at the site was 7 World Trade Center which opened in May 2006. The Lower Manhattan Development Corporation (LMDC), established in November 2001 to oversee the rebuilding process, organized competitions to select a site plan and memorial design. Memory Foundations, designed by Daniel Libeskind, was selected as the master plan, which included the 1,776-foot (541 m) 1 World Trade Center, three office towers along Church Street and a memorial designed by Michael Arad. Planning and construction The idea of establishing a World Trade Center in New York City was first proposed in 1946. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project3 but the plans were put on hold in 1949.4 During the late 1940s and 1950s, economic growth in New York City was concentrated in Midtown Manhattan, while Lower Manhattan was left out. To help stimulate urban renewal, David Rockefeller suggested that the Port Authority build a World Trade Center in Lower Manhattan.5 Initial plans, made public in 1961, identified a site along the East River for the World Trade Center.6 As a bi-state agency, the Port Authority required approval from both the governors of New York and New Jersey in order to undertake new projects. New Jersey Governor Robert B. Meyner objected to New York getting a $335 million project.7 Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate. At the time, ridership on New Jersey's Hudson and Manhattan Railroad (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958 after new automobile tunnels and bridges had opened across the Hudson River.9 In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes, the Port Authority offered to take over the Hudson & Manhattan Railroad to have it become the Port Authority Trans-Hudson (PATH). The Port Authority also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH.8 With the new location and Port Authority acquisition of the H&M Railroad, New Jersey agreed to support the World Trade Center project.10 Approval was also needed from New York City Mayor John Lindsay and the New York City Council. Disagreements with the city centered on tax issues. On August 3, 1966, an agreement was reached that the Port Authority would make annual payments to the City in lieu of taxes for the portion of the World Trade Center leased to private tenants.11 In subsequent years, the payments would rise as the real estate tax rate increased.12 Architectural design On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth & Sons as associate architects.13 Yamasaki devised the plan to incorporate twin towers; Yamasaki's original plan called for the towers to be 80 stories tall.14 In order to meet the Port Authority's requirement to build 10 million square feet (930,000 m2) of office space, the buildings would each need to be 110 stories tall.15 A typical floor layout and elevator arrangement of the WTC towersA major limiting factor in building height is the issue of elevators; the taller the building, the more elevators are needed to service the building, requiring more space-consuming elevator banks.15 Yamasaki and the engineers decided to use a new system with sky lobbies; floors where people could switch from a large-capacity express elevator which serves the sky lobbies, to a local elevator that goes to each floor in a section. This allowed the local elevators to be stacked within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of required elevator shafts.16.17 Altogether, the World Trade Center had 95 express and local elevators.18 This system was inspired by the New York City Subway system whose lines include local stations where local trains stop and express stations where all trains stop.19 Yamasaki's design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately 207 feet (63 m) in dimension on each side.1420 The buildings were designed with narrow office windows 18 inches (45 cm) wide, which reflected Yamasaki's fear of heights as well as his desire to make building occupants feel secure.21 Yamasaki's design included building facades sheathed in aluminum-alloy.22 The World Trade Center was one of the most striking American implementations of the architectural ethic of Le Corbusier and it was the seminal expression of Yamasaki's gothic modernist tendencies.23 In addition to the twin towers, the plan for the World Trade Center complex included four other low-rise buildings which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16 acres (65,000 m2) superblock.24 Structural design The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing the tube-frame structural system used in the twin towers. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority's Chief Engineer, oversaw the project.25 As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York including building codes. Nonetheless, the structural engineers of the World Trade Center ended up following draft versions of the new 1968 building codes.26 The tube-frame design, earlier introduced by Fazlur Khan, was a new approach which allowed open floor plans rather than columns distributed throughout the interior to support building loads as had traditionally been done. The World Trade Center towers utilized high-strength, load-bearing perimeter steel columns called Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces each consisting of three columns, three stories tall, connected by spandrel plates.26 The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.27 Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically so the column splices between adjacent modules were not at the same floor.26 The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads, providing lateral stability to the exterior walls and distributing wind loads among the exterior walls.28 The floors consisted of 4 inch (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers which helped reduce the amount of sway felt by building occupants. The trusses supported a 4-inch (100 mm) thick lightweight concrete floor slab with shear connections for composite action.29 Hat trusses (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building.30 Only 1 WTC (north tower) actually had an antenna fitted; it was added in 1978.31 The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.32 The tube frame design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind compared to traditional structures such as the Empire State Building that have thick, heavy masonry for fireproofing of steel structural elements.33 During the design process, wind tunnel tests were done to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.34 Experiments also were done to evaluate how much sway occupants could comfortably tolerate, however, many subjects experienced dizziness and other ill effects.35 One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level.36 Construction 1 World Trade Center and 2 World Trade Center under construction; Empire State Building and PanAm Building seen in Midtown, 1970In March 1965, the Port Authority began acquiring property at the World Trade Center site.37 Demolition work began on March 21, 1966 to clear thirteen square blocks of low rise buildings in Radio Row for construction of the World Trade Center.38 Groundbreaking for the construction of the World Trade Center took place on August 5, 1966.39 The site of the World Trade Center was located on landfill with the bedrock located 65 feet (20 m) below.40 In order to construct the World Trade Center, it was necessary to build the "bathtub" with a slurry wall along the West Street side of the site, serving to keep water from the Hudson River out.41 The slurry method devised by Port Authority’s chief engineer, John M. Kyle, Jr., involved digging a trench, and as excavation proceeded, filling the space with a "slurry" mixture composed of bentonite which plugged holes and kept water out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the "slurry" out. It took fourteen months for the slurry wall to be completed; it was necessary before excavation of material from the interior of the site could begin.42 The 1.2 million cubic yards (917,000 m3) of material excavated were used to expand the Manhattan shoreline across West Street to form Battery Park City (along with other fill and dredge material.)4344 In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers, and Karl Koch was hired to erect the steel.45 Tishman Realty & Construction was hired in February 1967 to oversee construction of the project.46 Construction work began on the North Tower in August 1968; construction on the South Tower was underway by January 1969.47 The original Hudson Tubes, carrying PATH trains into Hudson Terminal, remained in service as elevated tunnels during the construction process until 1971 when a new PATH station opened.48 The topping out ceremony of 1 WTC (North Tower) took place on December 23, 1970, while 2 WTC's ceremony (South Tower) occurred later on July 19, 1971.47 The first tenants moved into the North Tower in December 1970; the South Tower accepted tenants in January 1972.49 When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.50 The ribbon cutting ceremony was on April 4, 1973.51 Criticism Plans to build the World Trade Center were not without controversy. The site for the World Trade Center was the location of Radio Row, home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents, many of whom fiercely resisted forced relocation.52 A group of small businesses affected filed an injunction challenging the Port Authority's power of eminent domain.53 The case made its way through the court system to the United States Supreme Court; the Court refused to accept the case.54 The World Trade Center in July 2001Private real estate developers and members of the Real Estate Board of New York, led by Empire State Building owner Lawrence A. Wien, expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.5556 Others questioned whether the Port Authority really ought to take on a project described by some as a "mistaken social priority."57 The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups.5822 Lewis Mumford, author of The City in History and other works on urban planning, criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets."59 The twin towers' narrow office windows, only 18 inches (460 mm) wide, were disliked by many for impairing the view from the buildings.21 The trade center's "superblock", replacing a more traditional, dense neighborhood, was regarded by some critics as an inhospitable environment that disrupted the complicated traffic network typical of Manhattan. For example, in his book The Pentagon of Power, Lewis Mumford denounced the center as an "example of the purposeless giantism and technological exhibitionism that are now eviscerating the living tissue of every great city."60 On the other hand, Mr. Yamasaki saw the expanse as a focal point of serenity amidst the chaos of the city. For many years, the immense Austin J. Tobin Plaza was unwelcoming and often beset by brisk winds at ground level.61 In 1999, the outdoor plaza reopened after undergoing $12 million renovations which involved replacing marble pavers with gray and pink granite stones, adding new benches, planters, new restaurants, food kiosks and outdoor dining areas.62 In later years, the plaza became a center for outdoor concerts and other activities. Complex Twin towers The WTC site building arrangementWith the construction of 7 World Trade Center in the 1980s, the World Trade Center had a total of seven buildings, but the most notable were the main twin towers, which each were 110 stories tall, stood over 1,350 feet (410 m) high, and occupied about one acre (208.71 square feet) of the total 16 acres (65,000 m2) of the site's land. During a press conference in 1973, Minoru Yamasaki was asked, "Why two 110-story buildings? Why not one 220-story building?" His response was: "I didn't want to lose the human scale".63 When completed in 1972, 1 World Trade Center (the North Tower) became the tallest building in the world for two years (Chicago's Sears Tower set a new record when completed in 1974), surpassing the Empire State Building after a 40-year reign. The North Tower stood 1,368 feet (417 m) tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood 360 feet (110 m) tall. With the 360-foot-tall antenna/mast, the highest point of the North Tower reached 1,728 ft (527 m). 2 World Trade Center (the South Tower) became the second tallest building in the world when completed in 1973. The South Tower's rooftop observation deck was 1,377 feet (420 m) high and its indoor observation deck was 1,310 feet (399 m) high.64 The World Trade Center towers held the height record only briefly. Chicago's Sears Tower, finished in May 1973, reached 1,450 feet (442 m) at the rooftop.65 Of the 110 stories, eight were set aside for technical services in mechanical floors Level B5/B6 (floors 7/8, 41/42, 75/76, and 108/109), which are four two-floor areas evenly spaced up the building. All the remaining floors were free for open-plan offices. Each floor of the towers had 40,000 square feet (3,700 m2) of space for occupancy.18 Each tower had 3.8 million square feet (350,000 m2) of office space. Altogether the entire complex of seven buildings had 11.2 million square feet (1.04 km2) of space. The lobby of the World Trade CenterInitially conceived as a complex dedicated to companies and organizations directly taking part in "world trade," they at first failed to attract the expected clientèle. During the early years, various governmental organizations became key tenants of the World Trade Center including the State of New York. It was not until the 1980s that the city's perilous financial state eased, after which an increasing number of private companies—mostly financial firms tied to Wall Street—became tenants. During the 1990s, approximately 500 companies had offices in the complex including many financial companies such as Morgan Stanley, Aon Corporation, Salomon Brothers and the Port Authority itself. The basement concourse of the World Trade Center included The Mall at the World Trade Center along with a PATH station. Electrical service to the towers was supplied by Consolidated Edison (ConEd) at 13,800 volts. This service passed through the World Trade Center Primary Distribution Center (PDC) and sent up through the core of the building to electrical substations located on the mechanical floors. The substations "stepped" the 13,800 primary voltage down to 480/277 volt secondary power and further to 120/208 volt general power and lighting service. The complex also was served by emergency generators located in the sublevels of the towers and on the roof of 5 WTC.6667 The 110th floor of 1 World Trade Center (the North Tower) housed commercial and public service radio & television transmission equipment. The roof of 1 WTC contained a vast array of transmission antennas including the 360 ft (approx 110m) center antenna mast rebuilt in 1999 by Dielectric Inc. to accommodate DTV. The center mast contained the television signals for almost all NYC television broadcasters: WCBS-TV 2, WNBC-TV 4, WNYW 5, WABC-TV 7, WWOR-TV 9 Secaucus, WPIX 11, WNET 13 Newark, WPXN-TV 31 and WNJU 47. It also had four NYC FM broadcasters: WPAT-FM 93.1, WNYC 93.9, WKCR 89.9, and WKTU 103.5. Access to the roof was controlled from the WTC Operations Control Center (OCC) located in the B1 level of 2 WTC. Top of the World observation deck Midtown Manhattan from the observation deck of the south tower which received an estimated 80,000 visitors a day during the late 1990sAlthough most of the space in the World Trade Center complex was off-limits to the public, the South Tower featured a public observation area called Top of the World Trade Center Observatories on its 107th floor. When visiting the observation deck, visitors would first pass through security checks added after the 1993 World Trade Center bombing68 then were whisked to the 107th floor indoor observatory at a height of 1,310 feet (400 m). The Port Authority renovated the observatory in 1995, then leased it to Ogden Entertainment to operate. Attractions added to the observation deck included a simulated helicopter ride around the city. The food court was designed with a subway car theme.6970 Weather permitting, visitors could take two short escalator rides up from the 107th floor to an outdoor viewing platform at a height of 1,377 feet (420 m). On a clear day, visitors could see up to 50 miles (80 km) in any given direction.69 An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing and leaving the view unobstructed, unlike the observation deck of the Empire State Building.70 Windows on the World restaurant The view from Windows On The WorldThe North Tower had a restaurant on its 106th and 107th floors called Windows on the World, which opened in April 1976. The restaurant was developed by Joe Baum at a cost of more than $17 million.72 Aside from the main restaurant, two offshoots were located at the top of the North Tower: "Hors d'Oeuvrerie" (offered a Danish smorgasbord during the day and sushi in the evening) and "Cellar in the Sky" (a small wine bar).73 Windows on the World also had a wine school program run by Kevin Zraly. Windows on the World was closed following the 1993 World Trade Center bombing. Upon reopening in 1996, Hors d'Oeuvrerie and Cellar in the Sky were replaced with the "Greatest Bar on Earth" and "Wild Blue". In 2000, its last full year of operation, Windows on the World reported revenues of $37 million, making it the highest-grossing restaurant in the United States. Other buildings Twin Towers view from Empire State Building, May 2001Five smaller buildings stood around the 16 acre (65,000 m2) block. One was the 22-floor hotel which opened in 1981 as the Vista Hotel and in 1995 became the Marriott World Trade Center (3 WTC) at the southwest corner of the site. Three low-rise buildings (4 WTC, 5 WTC, and 6 WTC) in the same hollow tube design as the towers also stood around the plaza. 6 World Trade Center, at the northwest corner, housed the United States Customs Service and the U.S. Commodities Exchange. 5 World Trade Center was located at the northeast corner above the PATH station and 4 World Trade Center was at the southeast corner. In 1987, a 47-floor office building called 7 WTC was built north of the block. Beneath the World Trade Center complex was an underground shopping mall which in turn had connections to various mass transit facilities including the New York City Subway system and the Port Authority's own PATH trains connecting Manhattan to Jersey City, Hoboken, and Newark. One of the world's largest gold depositories was stored underneath the World Trade Center, owned by a group of commercial banks. The 1993 bomb detonated close by but the vault held. Seven weeks after the September 11 attacks, $230 million in precious metals were removed from basement vaults of 4 WTC which included 3,800 100-Troy-ounce registered gold bars and 30,000 1,000-ounce silver bars.75 Category:Modern Category:Famous Building Category:9/11 attacks